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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

THE EARTHQUAKE ADVANCE THEORY         169>
since 1899, there has been no interruption as great as the advance of the Hidden Glacier in 1906 or 1907.
In 1905 evidence was found to prove that Galiano Glacier had undergone great changes, since last observed and photographed in 1891. Its moraine-covered surface had been so broken as to completely destroy an alder and cottonwood thicket that grew on it in 1890 and 1891, but ablation had healed the broken surface so that one could easily travel over it in 1905. There is some evidence that the front of the ice bulb advanced, and sound basis for the inference that there was lateral spreading toward the valley walls, destroying marginal drainage. The changes in the glacier condition extended to a hitherto undiscovered, stagnant, off-lying ice mass on which an alluvial fan had been deposited,, and by the advance this fan was destroyed and its place in large part taken by morainic mounds thrust up through it. We have no means of positively determining in which of the fourteen years between 1891 and 1905 these changes occurred but photographs make it certain that it was after 1895, and we infer that it was in 1900 or 1901 because of the age of the alder bushes that have again begun to grow on the moraine. Other facts indicate recency of the change, such for example as the imperfect redevelopment of marginal drainage, and of the alluvial fan between the morainic knolls. Furthermore, we are at a loss to explain the transformation of this glacier on any other hypothesis than the effect of earthquake shaking, and are forced to the conclusion that the advance is the result of a response to the shaking during the earthquakes in September, 1899. The Galiano Glacier, whose response was so rapid, is a very short glacier, with steep valley sides and head, on which in September deep snows had already been added to the extensive snowfields and steeply-descending glaciers. Evidence that there has been extensive avalanching from these steep slopes was readily discovered by a comparison of the 1891 photographs with the condition in 1905; and even in 1909 the spaces from which large masses of ice had fallen after 1891 were not yet reoocupied by ice.
It seems probable, though the facts do not conclusively prove it, that other small glaciers, similar to Galiano Glacier, had undergone a like change a short time before the expedition of 1905. Had we then had suspicion of the possibility of such glacier transformation we might have discovered evidence which is now obscured by ablation. The glaciers which gave the best indication of having undergone changes similar to those of the Galiano are McCarty, Hendrickson and Rasmussen Glaciers on the west side of Russell Fiord, and the Blossom Island Glacier just north of Blossom Island east of Marvine Glacier. It is probable that some of the small glaciers have failed to show evidence of notable response to earthquake shaking because of the small supply of snow and ice thrown down upon them. Of one such glacier, the Black Glacier, the one nearest the Galiano, the evidence is convincing that there has been no distinct advance of the end, no pronounced lateral spreading, nor sufficient breaking of the surface to destroy the alder growth upon it. Not having yet advanced as a result of the 1899 earthquakes, we assume that this and other similar glaciers will probably not do so in the future.
In 1906 four glaciers, the Haenke, Atrevida, Variegated, and Marvine, had become absolutely transformed from their condition in 1905. Three of these glaciers are of about the same order, and it seems natural that they should advance essentially together. Moreover, their size is such in comparison with the Galiano that it is not difficult to understand why they should require so much longer to respond to the earthquake